1. Field of the Invention
The present invention relates to a diode laser pumped solid-state laser amplifier that uses a diode laser as an pumping source, and to a diode laser pumped solid-state laser.
2. Description of the Related Art
FIG. 17 is a diagram showing the structure of a pumping module employed in a conventional diode laser pumped solid-state laser amplifier that is described in a literature, for example, “Solid-state Laser Engineering” (Springer-Verlag, P.348). In the drawing, two diode laser arrays 3 are fixed to one flank of a heat sink 5 shaped like a triangular prism with light-emitting portions 4 thereof directed in the left-hand direction in FIG. 17. A cylindrical lens 34 for converging pumping light rays emanating from the diode laser arrays 3 is fixed to the tips of the light-emitting portions 4. An electric cooler 301 for adjusting the temperature of the heat sink 5 is fixed to the bottom on the opposite side of the heat sink 5. A heat exchanger 302 for removing heat from the diode laser arrays 3 via the heat sink 5 and electric cooler 301 is fixed to the electric cooler 301.
Cooling water is circulated through the heat exchanger 302, whereby the heat exchanger exchanges heat with the diode laser arrays 3 via the heat sink 5. Since the electric cooler 301 is interposed between the heat exchanger 302 and heat sink 5, once the heat sink 5 is cooled using the electric cooler 301, the temperature of the diode laser arrays 3 can be adjusted quickly without any change in temperature of the cooling water to be circulated through the heat exchanger 302.
The two diode laser arrays 3 are fixed to the heat sink 5 while oriented in the same direction. The cylindrical lens 34 is fixed to the faces of the light-emitting portions 4 of the diode laser arrays 3. Pumping light-rays emanating from the light-emitting portions 4 are therefore converged by the cylindrical lens 34. Moreover, the electric cooler 301 is interposed between the heat sink 5 and heat exchanger 302, the wavelength of pumping light rays emanating from the diode laser arrays 3 can be adjusted by adjusting the temperature of the heat sink 6 using the electric cooler 301. The components of the heat sink 5, diode laser arrays 3, cylindrical lens 34, electric cooler 301, and heat exchanger 302 constitute one pumping module 90.
FIG. 18 is an oblique view showing a state in which the pumping modules 90 each having the components shown in FIG. 17 are fixed to a support plate 303 together with a solid-state laser rod 1 and flow tube 2. In this structure, one solid-state laser rod 1 is encircled by four pumping modules 90. Each pumping module 90 has the end surface of the heat sink 5 thereof fixed to the support plate 303, and has thus one end thereof supported. The light-emitting portions of the diode laser arrays 3 fixed to the four pumping modules 90 are directed toward the axial core of the solid-state laser rod 1. Pumping light rays emanating from the light-emitting portions 4 are each affected by the cylindrical lenses 34 so that a point of condensing is located on the axial core of the solid-state laser rod 1. The solid-state laser rod 1 is sheathed by the flow tube 2. A cooling medium flows through a space created between the solid-state laser rod 1 and flow tube 2, whereby the solid-state laser rod 1 is cooled.
In a device for pumping the solid-state laser rod 1 using pumping light and amplifying light passing through the solid-state laser rod 1, generally, when the distribution of heat dissipation levels on a section of the laser rod becomes inhomogeneous, a bifocal phenomenon or a phenomenon that the focal length of the laser rod becomes different from local point to local point on a section of the laser rod takes place while the solid-state laser rod 1 is exerting a lens effect due to heat dissipation. When the bifocal phenomenon takes place, it becomes impossible to sufficiently correct the lens effect of the solid-state laser rod 1 with the employment of an ordinary optical element such as a spherical mirror, convex lens, or concave lens. This poses a problem that the performance of amplification of high-quality laser beam deteriorates and stability is impaired.
In the conventional diode laser pumped solid-state laser amplifier having the foregoing components and using a diode laser as a pumping source, unlike the one using an arc lamp as a pumping source, no special care has been taken of the homogeneity of the distribution of heat dissipation levels on a section of the laser rod.